1. Field of the Invention
The present invention relates to a high-frequency circuit board unit, a high-frequency module using the same unit, and an electronic apparatus using the same module. The invention also relates to a manufacturing method for the above-described high-frequency circuit board unit.
2. Description of the Related Art
FIG. 11 is a sectional view illustrating a conventional high-frequency circuit board unit. In FIG. 11, a high-frequency circuit board unit 1 includes a circuit board 2, a semiconductor device 8, and a filter 15 which serves as a passive impedance circuit device. The circuit board 2 has a dielectric substrate 3, which is formed of a dielectric material, such as an alumina substrate, having a comparatively low dielectric constant (of about 9 to 10). A ground electrode 4 and terminal electrodes 5a, 5b are formed on a first main surface of the dielectric substrate 3. Wiring electrodes 6a, 6b, 6c, 6d are formed on a second main surface of the dielectric substrate 3. The wiring electrodes 6a, 6d are connected respectively to the terminal electrodes 5a, 5b via respective through-holes 7a, 7b. The semiconductor device 8 is mounted on the second main surface of the dielectric substrate 3, and the wiring electrodes 6a, 6b are connected respectively to connecting lands 8b, 8a formed on the semiconductor device 8 via wires (bonding wires) 10. The filter 15 is mounted on the wiring electrode 6c formed on the second main surface of the dielectric substrate 3. The filter 15 is formed of a dielectric substrate 16 and a strip line electrode 17 is formed on the wiring electrode 6c and provided with a filtering function. The strip line electrode 17 and the wiring electrode 6d are connected to each other via a wire 10.
According to the high-frequency circuit board unit 1 constructed as described above, both the semiconductor device 8, which is an active device, and the filter 15, which is a passive device, are mounted on the circuit board 2. Accordingly, the circuit board unit 1 can be operated as a component having one function.
Generally, however, the semiconductor device 8, in particular, a GaAs semiconductor device, has a low breakdown voltage, and an electrostatic surge voltage may cause electrostatic discharge damage to the semiconductor device 8. Accordingly, in the high-frequency circuit board unit 1, if, for example, an electrostatic surge voltage is applied to the semiconductor device 8 via a signal line formed of the terminal electrode 5a, the through-hole 7a, the wiring electrode 6a, and the wire 10, the high-frequency circuit board unit 1 may be damaged.
In particular, in a wireless-communication transceiver module using such a high-frequency circuit board unit, a terminal electrode connected to an antenna is exposed. Thus, if a surge voltage is applied to the circuit board unit via this terminal electrode, the semiconductor device may be damaged.
On the other hand, a surge voltage applied to the terminal electrode 5b via the filter 15 does not damage the semiconductor device 8 as long as the filter 15 is provides insulation between the input and output terminals.
Thus, in a semiconductor assembly line, for example, in which the semiconductor device 8 is mounted on the circuit board 2, sufficient measures must be taken against electrostatic damage regardless of the presence or the absence of the filter 15. However, this increases the cost of carrying out the process steps.
One way of protecting against electrostatic damage is to connect a surge-voltage protecting diode to a signal terminal of a semiconductor device. With this measure, however, the semiconductor device becomes expensive, and the diode may cause the loss of a high-frequency signal.